Prevention of corrosion of wet metal articles



June 21,

M. ZIMMERMANN 3,257,159

PREVENTION OF CORROSION OF WET METAL ARTICLES Filed Jan. 8, 1965 mg/ I INVENTOR.

MAX Z IMMERMANN W WW7 A TTORNEY carbon.

. gen present.

United States Patent ,81 19 Claims. (Cl. 212.7)

The present invention relates to the prevention of corrosion of wet metal articles, and more particularly to a process for the wet preservation and corrosion protection of metal articles which are in contact with an aqueous phase and to preparations for such purposes.

The use of hydrazine as a corrosion protective agent, for example in steam boilers, hot water plants, etc. is already known. The effect of this compound is attributed to the reactivity which has long been known to exist between hydrazine and the oxygen dissolved in water. In

addition, however, it is assumed that hydrazine has an effect on the formation of a protective layer on metal surfaces. In articles made of iron, this effect is explained by the formation of a very thick, firmly adhering layer of Fe O A-t normal temperature, the rate of reaction of hydrazine with oxygen is very low. The effect of hydrazine as a corrosion protective agent, especially on bare metal surfaces, leaves much to be desired, especially if chlorides or sulfates are dissolved in the water.

It has already been proposed to enhance the effect of hydrazine by adding activating substances such as active However, the effect of the active carbon is limited to the accelerated reaction of hydrazine with the oxy- In other words, this effect is limited substantially to the removal of oxygen from the water which i e is used for the operation of the steam boilers, etc.

It is an object of the present invention to overcome previous drawbacks encountered in the prevention of corrosion of wet metal articles, and to provide for the more effective prevention of corrosion of wet metal articles.

A further object of the present invention is to provide a'method for the wet preservation and corrosion protection of metal articles which are in contact with an aqueous phase normally corrosive thereto, especially after prolonged contact therewith, using a particular mixture of ingredients having a combined beneficial effect.

It is a further object of the present invention to provide a preparation containing a mixture of ingredients which may be added to an aqueous phase, such as an oxygen containing water and/or a salt containing water, in predetermined dosages for attaining the wet preservation and corrosion protection of such metal articles which may be in contact with the aqueous phase.

Other and further objects will become apparent from a study of the within specification and accompanying examples in which:

FIG. 1 shows a graph illustrating the reaction between hydrazine and oxygen in an open system over an extended period of time in the presence or absence of complex heavy metal alkali cyanides, and

FIG. 2 shows a graph illustrating the reduction in oxygen content in a closed system by reason of the presence of hydrazine in the presence or absence of complex heavy metal alkali cyanides.

It has now been found in accordance with the present invention that a process for the wet preservation and corrosion protection of metal articles in contact with an aqueous phase may be provided by means of hydrazine in the presence of activating substances, according to which hydrazine (preferably hydrazine hydrate) is added Patented June 21, 1966 in quantities of 0.1 to 3000 mg./liter of water and complex heavy metal cyanides are added in quantities of 0.1 to 10 mg./liter, preferably 0.1 to 5 rug/liter of water to the aqueous phase in contact with such metal articles.

Complex cyanides of monovalent copper, trivalent cobalt, divalent nickel, monovalent silver and divalent iron have proved to be especially effective. The complex cyanides are used in the form of their alkali metal (e.g. sodium, potassium and lithium) compounds or their ammonium compounds. The heavy metal cyanides must be present in a form which has no oxidizing effect on hydrazine. The complex-forming metals are therefore used in the lowest stage of oxidation in which they are stable under normal conditions. 7

In accordance with the present invention, it has been ascertained that the protective action of hydrazine can be increased considerably at normal temperature by the addition of the complex heavy metal cyanides, whereby to remove effectively oxygen from the aqueous phase in question. In addition, a good corrosion protection can also be achieved on bare metal surfaces, i.e. Where a protective layer is not already present.

Significantly, in the absence of oxygen, the above-mentioned complex heavy metal cyanides have no activating effect on the autooxidation of hydrazine in aqueous solution. This was established by way of a series of experiments, in which an aqueous solution of hydrazine free from oxygen and containing mg. of hydrazine per liter was treated in each case with 10 mg./liter of one of the complex heavy metal cyanides of Na [Cu(CN)4], K [Ni(CN) and Na.,[Fe(CN) in a container thereafter closed to exclude air and left to stand in this manner over a period of 14 days. The hydrazine content was then determined by iodometric titration. No additional increase in breakdown of hydrazine could be detected over that of the blank test used as control, in which a slight drop in the hydrazine concentration occurred due to autooxidation, nor could any ammonia be detected.

However, it was found also that the rate of reaction of hydrazine with oxygen in an open system was considerably increased by the addition of the complex cyanides as covered in the graph of FIGURE 1. Here again, in a series of tests, 10 mg./liter of monovalent Cu in the form of Na [Cu(CN) ]Curve 5and divalent Fe in the form of Na [Fe(CN) ]curve 4and divalent cobalt in the form of Na ['Co(CN)e]curve 3 and divalent Ni in the form of Na [Ni(CN)4]curve 2were added to separate portions of an aqueous solution containing 100 mg. of N2'H4 per liter in open beakers of Jen-aer glass. The beakers, together with a similar control beaker containing a blank sample without addition of cyanide complexes were left to stand uncovered at 20 'C. and the decomposition of hydrazine was followed over a period of 50 hours. It was found that in the blank sample-curve 198 mg./liter of the original 100 mg./ liter of N H were still present after 48 hours whereas, for example, the hydrazine concentration was reduced to 44 mg./liter by the addition of the monovalent copper-complex (see FIGURE 1). This establishes the marked effectiveness of the corresponding cyanide in the removal of oxygen present in the aqueous phase in an open system.

FIGURE 2 shows the reduction of oxygen by hydrazine in the presence of cyanide complexes in a closed system at normal temperature (20 (3.). In this experiment, water which was supersaturated with oxygen to provide an 0 concentration initially of 40 mg./ liter, was kept in a closed measuring flask and in addition, mg. of hydrazine per liter were added in the form of a 24% solution of hydrazine hydrate and 10 mg./ liter of copper, iron and nickel, respectively, were added in the form of their complex alkali cyanides. The reduction in oxygen was then measured by the same method as in the examples of FIGURE 1 by polarographic determinations over a period of 24 hours. FIGURE 2, which covers a closed system, shows the same type of results as FIGURE 1, which covers an open system. The reduction in oxygen in each instance is considerably greater than that in the blank sample due to the presence of the heavy metal cyanides. In FIGURE 2 curve 1 denotes the blank, curve 2 the example with the addition of Ni(II) in the form of Na [Ni(CN) curve 4 the addition of Fe(lI) in the form of K [Fe (CN) and curve the addition of Cu(I) in the form of Na [Cu(CN)4].

For corrosion protection, in addition to the increased reduction in oxygen, the influence of the activators together with hydrazine on an accelerated formation of a protective layer on the metal surfaces is also of importance since it was found that the heavy metal complexes of nickel and silver which, compared with the corresponding copper complexes, have a relatively very low effect on the reduction in oxygen, show approximately the same effect as such other heavy metal complexes (e.g., copper complexes) in corrosion protection tests.

It was found that blank iron surfaces (iron pipes filled with tap-water) showed a black film being a layer of iron oxide-Fe O if to the water there was added bydrazine with one of the aforementioned nickel or silver complexes, whereas the iron pipes filled with tap-water alone showed only a sludge of red-orange iron oxide Fe O at the bottom. Without the addition of the activated hydrazine however corrosion of the iron surfaces had occurred and more than 0.1 g. of iron per day and square meter had been corroded away, whereas with the addition of the activated hydrazine the corrosion amounted only to a value of below 0.001 g./m d.

To carry out the process of the present invention, the quantity of hydrazine calculated to give a concentration of 0.1 to 3000 mg./liter in water is added, preferably in the form of 24% hydrazine hydrate, to the feed or cooling water, etc., which is in contact with the metal to be protected. In this regard a concentration of about 0.1 mg./liter water is sufiicient for degasified feed water, for example in boilers, whereas a concentration of about 300 rug/liter is preferred for water used in cooling circuits which generally contains a significant quantity of oxygen therein. Higher hydrazine contents are not harmful in accordance with the present invention but are avoided normally because of economical considerations.

-In addition, the complex heavy metal cyanides are added, preferably in the form of aqueous solutions of their alkali' metal or ammonium compounds. A sufiicient protective effect is provided if the complexes are present in quantities of 0.01 to 10 mg./liter water calculated on the metal. It is preferred, however, to use a quantity of 0.1 to 5.0 mg/liter water.

In this connection it will be appreciated that the heavy metals of Groups 1b7b and 8, which form water-soluble alkali metal cyanide complexes and which metals are not reduced by hydrazine under the resulting conditions to the metal itself may be used in the form of their alkali cyanide complexes such as those of the heavy metals: copper, silver, zinc, cadmium, tungsten, chromium, manganese, iron cobalt and nickel.

As for the counterpart of the complex cyanide, the same may comprise an alkali component which may be defined as an alkali metal, such as sodium, potassium, lithium, etc., or ammonium. Among the specific compounds usable herein as complex heavy metal cyanides, therefore, are Na [Cu(CN) K [Cu(CN) In practice, it is advantageous to prepare mixtures of hydrazine hydrate and the cyanide complexes used, these mixtures being then used in suitable doses depending on the purpose and the type of water to be treated, and its oxygen or salt content, etc. After this first preservation, it is then usually sufiicient merely to maintain the necessary hydrazine concentration by adding subsequent doses of hydrazine hydrate. To preserve a static system, one single dose of the mixture added to the water is usually sufficient.

In cooling systems it is generally not necessary to remove all the oxygen content of the water, since the hydrazine and the nickel complex present in the water develops and preserves a corrosion resistant layer on the metal surfaces. The addition of the copper complex is advantageous in the case of water which has a higher oxygen content, which oxygen is to be removed.

Most preferably the copper cyanide complexes are used in systems containing water having a temperature below 60 C. At temperatures above 60 C. the nickel, cobalt and iron complexes are preferred, since they are more stable towards reduction by hydrazine.

' The present process can therefore be used advantageously for the wet preservation and corrosion protection of steam producers, hot water plants, coolers using water as circulating medium and heat exchangers. It is especially advantageous that the preserving effect occurs at water temperatures at which only insuflicient protection of the metal surfaces was produced by the methods hitherto used, i.e., at temperatures of below C. or more precisely below the boiling point of the water up to the freezing point, however this temperature is no limitation of the new process for the hydrazine mixed with the aforesaid complex cyanides is applicable also to systems containing hot water or hot water and steam.

The following examples are set forth by way of illustration and not limitation:

EXAMPLE 1 This test shows the effect of the cyanides on the degree of protection against corrosion of bare metal surfaces. Pieces of boiler tubes or rings of iron quality St. 35.29 were annealed for 2 hours at 600 C. without tension and pickled until bare in 10% hydrochloric acid containing 0.1% of urotropin (hexamethylene tetramine). The pretreated rings were suspended in an aqueous solution containing 200 mg. of N H per liter and 100 mg. of NaCl per liter. The addition of sodium chloride served to increase the corrosive action of the water. The samples were kept for 14 days in Erlen meyer flasks closed with rubber stoppers. Sample 1 contains no activator additive, and Sample 2 contains 0.5 mg. of Na [Cu (CN) per liter. While Sample 1 undergoes pitting with severe corrosion, Sample 2 shows a black layer of Fe O without any pitting.

EXAMPLE 2 EXAMPLE 3 A heating circuit charged with ordinary salt-containing water having an N H concentration of 100 mg. per

liter and containing 0.5 g./liter of Ni as activator additive in the form of the ('NH [Ni(CN) complex shows no sign of corrosion after being left to stand over the summer and can be put into operation again with the .water thus treated.

EXAMPLE 4 A closed cooling circuit containing softened or fully desalted water which has been treated with the addition corrosion protection of metal articles, such as those made of ferrous metals, in contact with an aqueous phase such as water containing oxygen and/ or inorganic salts such as chlorides, sulfates and nitrates of the alkali and alkaline earth metals, which comprises providing in such aqueous phase which is in contact with the particular metal article, both hydrazine in an amount substantially between about 0.13000 mg./liter and a complex heavy metal cyanide in an amount, calculated on the heavy metal, substantially between about 0.01-10 mg./liter. Preferably, the hydrazine is used in the form of hydrazine hydrate, as for example in the form of substantially about a 24% solution, and the complexheavy metal cyanide is present preferably in an amount,

calculated on the heavy metal, substantially between about 0.1- mg./liter of the aqueous phase.

In accordance with a preferred embodiment of the present invention, the complex heavy metal cyanide is selected from the group consisting of the alkali metalmonovalent copper-cyanide, alkali metal-trivalent cohalt-cyanide, alkali metal-divalent nickel-cyanide, alkali metal-monovalent silver-cyanide, alkali metal-divalent iron-cyanide, ammonium-monovalent copper-cyanide, am-

monium trivalent cobalt cyanide, ammonium divalent nickel cyanide, ammonium monovalent silver cyanide, ammonium-divalent iron-cyanide, and mixtures thereof. More specifically, typical complex heavy metal cyanides include In another sense, the present invention represents an improvement in the method for the wet preservation and corrosion protection of predominantly iron-containing metals in contact with a solution containing at least one of oxygen and salt which normally cause corrosion, which improvement comprises maintaining in such solution when in contact with the particular rnetal article, a mixture of hydrazine and a complex heavy metal cyanide in ac cordance with the foregoing.

Moreover, the present invention relates to a preparation for the wet preservation and corrosion protection of metal articles in contact with an aqueous phase, such preparation comprising a mixture in an aqueous solution of hydrazine and a complex heavy metal cyanide in amounts per liter as stated above. Such preparation contemplates complex heavy metal cyanides such as those selected from the foregoing enumerated group and in particular preparations may be used which contain in aqueous solution a mixture of hydrazine in an amount substantially between about 0.1-3000 mg./liter with substantially between about 0.01- mg./liter, calculated on the particular heavy metal, of Na Cu(CN) It will be appreciated that the instant specification and drawings are set forth by way of illustration and not limitation, and that various modifications and changes may be made without departing from the spirit and scope of the present invention which is to be limited only by the scope of the appended claims.

- 3000 mg./liter and a complex heavy metal cyanide in an anrount, calculated on the heavy metal, substantially between about 0.01-10 mg./1iter.

2. Method according to claim 1 wherein the hydrazine is used in the form of hydrazine hydrate.

3. Method according to claim 2 wherein said hydrazine hydrate is in the form of substantially abouta 24% solution.

4. Method according to claim 1 wherein said cyanide is present in an amount, calculated on the heavy metal, substantially between about 0.l- 5 mg./liter of the aqueous phase.-

5. Method according to claim 1 wherein said complex heavy metal cyanide is selected from the group consisting of alkali metal-monovalent copper-cyanide, alkali metaltrivalent cobalt-cyanide, alkali metal-divalent nickel-cyanide, alkali metal-monovalent silver-cyanide, alkali'metaldivalent iron-cyanide, ammonium-monovalent copper-cyanide, ammonium-trivalent cobalt-cyanide, ammonium-divalent nickel-cyanide, ammonium-monovalent silver-cyanide, ammonium-divalent iron-cyanide, and mixtures thereof.

6. Method according to claim 1 wherein said complex heavy metal cyanide is Na [Cu(CN) 7. Method according to claim 1 wherein said complex heavy metal cyanide is K [Cu(CN) 8. Method according to claim 1 wherein said complex heavy metal cyanide is (NH [Ni(CN)4].

9. Method according to claim 1 wherein said complex heavy metal cyanide is Na Ni(CN) 10. Method according to claim 1 wherein said complex heavy metal cyanide is Na [Fe(CN) 11. In the method for the wet preservation and corrosion protection of predominantly iron-containing metal articles in contact with an aqueous solution containing at least one of free oxygen and an inorganic salt which normally cause corrosion, the improvement which comprises maintaining in said aqueous solution when in contact with the particular metal article, a mixture of hydrazine in an amount substantially between about 0.1-3000 mg./ liter and a complex heavy metal cyanide in an amount, calculated on the heavy metal, substantially between about 0.01-10 mg./liter.

12. Improvement according to claim 11 wherein the hydrazine is used in the form of substantially about a 24% hydrazine hydrate solution and said cyanide is present in an amount, calculated on the heavy metal, substantially between about 0.l-5 mg./liter of the aqueous phase.

13. Preparation for the Wet preservation and corrosion protection of metal articles in contact with an aqueous phase which comprises a mixture in aqueous solution of hydrazine in an amount substantially between about 0.1- 3000 mg./liter and a complex heavy metal cyanide in an amount, calculated on the heavy metal, substantially between about 0.0l10 mg./liter.

14. Preparation according to claim 13 wherein the hydrazine is present in the form of substantially about a 24% hydrazine hydrate solution and said cyanide is present in an amount, calculated on the heavy metal, sub stantially between about 0.1-5 mg./kg. of the 24% hydrazine hydrate solution present.

15. Preparation according to claim 14 wherein said complex heavy metal cyanide is selected from the group consisting of alkali metal-monovalent copper-cyanide, alkali metal-trivalent cobalt-cyanide, alkali metal-divalent nickel-cyanide, alkali metal-monovalent silver-cyanide, alkali metal-divalent iron-cyanide, ammonium-monovalent copper-cyanide, ammonium-trivalent cobalt-cyanide, ammonium-divalent nickel-cyanide, ammonium-monovalent silver-cyanide, ammonium-divalent iron-cyanide, and mixtures thereof.

16. Preparation for the wet preservation and corro sion protection of metal articles in contact with an aqueous phase which comprises a mixture in aqueous solution 7 of hydrazine in an amount substantially between about 0.1-3000 mg./liter and Na Cu(CN) in an amount, calculated on the copper, substantially between about 0.01- 10 mg./liter.

17. Preparation for the wet preservation and corrosion protection of metal articles in contact with an aqueous phase which comprises a mixture in aqueous solution of hydrazine in an amount substantially between about 0.1- 3000 mg./liter and (NH Ni(CN) in an amount, calculated on the nickel, substantially between about 0.01- 10 mg./liter.

18. Preparation for the wet preservation and corrosion protection of metal articles in contact with an aqueous phase which comprises a mixture in aqueous solution of hydrazine in an amount substantially between about 0.1- 3000 mg./liter and Na Ni(CN) in an amount, calculated on the nickel, substantially between about 0.01-10 mg./ liter.

19. Preparation for the wet preservation and corrosion protection of metal articles in contact with an aqueous phase which comprises a mixture in aqueous solution of hydrazine in an amount substantially between about 0.1- 3000 mg./liter and Na Fe(CN) in an amount, calculated 5 on the iron, substantially between about 0.0ll0 mg./ liter.

References Cited by the Examiner UNITED STATES PATENTS 1,260,740 3/1918 Allen l486.l4 2,901,437 8/1959 Bailey et al. 252389 X 3,151,087 9/1964 Ryznar et al 252387 X 

1. METHOD FOR THE WET PERSERVATION AND CORROSION PROTECTION OF METAL ARTICLES IN CONTACT WITH AN AQUEOUS PHASE WHICH COMPRISES PROVIDING IN SUCH AQUEOUS PHASE WHICH IS IN CONTACT WITH THE PARTICULAR METAL ARTICLE, BOTH HYDRAZINE IN AN AMOUNT SUBSTANTIALLY BETWEEN ABOUT 0.13000 MG./LITER AND A COMPLEX HEAVY METAL CYANIDE IN AN AMOUNT, CALCULATED ON THE HEAVY METAL SUBSTANTIALLY BETWEEN ABOUT 0.01-10 MG./LITER. 